The invention relates to a liquid ring gas pump having one or more stages, which each have a working space, an impeller eccentrically mounted therein, control discs that bound the working space axially on both sides, and adjacent ducts or chambers for the supply and discharge of the conveyed gas to and from the working space, the control discs being formed identically to each other with identical suction and pressure openings.
In liquid ring gas pumps, an impeller rotates within an eccentrically circulating liquid ring. During the circulation, the liquid ring penetrates to a greater or lesser extent into the cells formed between the vanes of the impeller. As a result, the free volume in the impeller cells is alternately enlarged and reduced. In that region of the revolution in which the cell volume is enlarged, the suction opening, through which the gas to be conveyed is taken into the cells, is located at the end in a control disc. In the end region of that part of the revolution in which the compression is carried out, there is the pressure opening, through which the compressed gas in the pressure space of the pump is exhausted.
Liquid ring gas pumps are employed both as a vacuum pump, where they convey the gas compressed from a negative pressure to approximately atmospheric pressure, and also as a compressor, in which they convey the gas compressed from atmospheric pressure to a positive pressure. There are liquid ring gas pumps as single-stage and multi-stage designs. Single-stage liquid ring gas pumps can be applied as a vacuum pump in the upper coarse vacuum or as a compressor, on account of the lower compression ratio. Two-stage machines have their preferred range of use as a vacuum pump in the lower pressure range of the vacuum.
The working spaces in which the impeller rotates and in which the liquid ring is built up are bounded axially on one side or on both sides by a control disc. In the case of multi-stage liquid ring pumps, these working spaces with impeller and control discs are arranged one after another axially in an appropriate number.
Traditionally, a liquid ring gas pump comprises a large number of components which are arranged on one another in the axial direction during the pump assembly. The supporting surfaces of the individual components are at the same time sealing surfaces of the machine from the pump interior to the environment. Axially on the outside, the control discs are adjoined by the outer housings, in which the ducts or chambers for the guidance of the gas and liquid streams are contained. Surfaces which in turn have to be sealed off are also present between the control discs and the outer housings.
The control discs have openings which ensure the inflow and outflow of the conveyed gas from the outer compressor housing to and from the working space. Depending on the number of stages and the design of the liquid ring gas pump, one or two openings are provided in these control discs for the inflow (suction opening) and outflow (pressure opening) of the conveyed medium. Because of the compression of the gas in each liquid ring stage, the pressure opening is generally designed to be smaller than the suction opening. The exact position and the geometric contours of the openings have a great influence on the achievable intake volume flow and the efficiency. Therefore, the shape and size of the suction and pressure openings also differ in practice.
In the case of this classical pump design, the control discs are implemented differently in design terms. For example, in the two-stage pump, each of the four control discs has a different geometry. The two axially outer control discs each have a suction and a pressure opening; the central control disc of the first stage has only the pressure opening, and the central control disc of the second stage has only the suction opening. Since, conventionally, the control discs are implemented as cast parts, even the two outer control discs are different in design terms, since the openings and the centering means with respect to the housing are arranged in mirror-image fashion. The disadvantage of this conventional pump design is the large number of different components, which cause a high degree of complexity in production, the purchasing of raw parts, the machining of parts and the stockholding. High unit and processing costs are the result.
Already known are first approaches to configuring the control discs more simply as flat discs with a constant thickness (EP 0 678 674 A2). This makes it possible to design symmetrical control discs as a standard component. In production, these control discs can be punched out of flat metal sheets or machined using laser technology. In addition, it is frequently necessary to adapt the adjacent flow ducts in the adjacent housing parts in such a way that the optimum flow conditions are achieved. For example, in the prior art cited, the outlet from the working space in the pressure slot is of a stepped design, by which means a curved flow duct is approximately modeled.
Entirely standard control discs, which are designed as flat components, have previously been used only in single-stage liquid ring gas pumps, since, with a standard configuration, these always have a suction opening and a pressure opening (DE 10 57 274 B, DE 197 58 340 A1). For instance, for multi-stage pumps in which the central control discs have only one opening in each case, at least three different designs of the control discs would be necessary.
The object of the invention is to provide a liquid ring gas pump of the type in which the number of different control discs is reduced.